1. Technical Field of the Invention
The present invention relates to a silicon dioxide-coated polyolefin resin and a process for its production.
2. Prior Art
Polyolefin resins have a wide variety of uses arising from their excellent properties. For example, the polyolefin resin composed of a cyclopentene-based polymer described in Japanese Unexamined Patent Publication No. 168625 of 1994 has excellent electrical resistance and low water absorption, and therefore exhibits the feature of dimensional stability even under highly humid conditions. The polyolefin resin composed of a norbornene-based open-ring polymer described in Japanese Unexamined Patent Publication No. 152549 of 1998 has excellent optical properties, including transparency, water resistance and birefringence.
These polyolefin resins are widely used in optical parts, electronic parts, automobile parts and the like because of their excellent properties, but since they lack functional groups and therefore generally have low adhesion to other coatings or materials, it is difficult to form coating layers over their surfaces and this has hampered efforts to take full advantage of their excellent properties.
In particular, polyolefin resins offer considerable potential advantages for use in magnetic recording media and other electronic devices where their excellent properties such as low moisture absorption, heat resistance and chemical resistance are utilized, but formation of highly adhesive and durable coating layers could further increase their potential advantages as base materials for electronic devices and other devices having layers consisting of magnetic recording media additionally formed over the coating layers.
It is therefore an object of the present invention to establish a process for formation of an organic silicon-based coating with high adhesive property to polyolefin resins and high durability.
These objects of the invention can be achieved by the following construction.
Specifically, it is a process for production of a silicon dioxide-coated polyolefin resin wherein, after hydrophilic treatment of the surface of a polyolefin resin, it is coated with a primary coating composed of an organic silicon compound and the base is then contacted with a solution containing silicofluoric acid with silicon dioxide in a supersaturated state, to form a silicon dioxide coating on the primary coating.
The primary coating is preferably obtained by applying and subsequently drying a coating solution containing a silicon compound or its hydrolysate with an organic functional group represented by the following general formula (1)
R1nSi(R2)4xe2x88x92nxe2x80x83xe2x80x83(1)
where R1 is an organic functional group with a methacryloxy group,
R2 is one or a plurality of hydrolyzable groups selected from among alkoxyl groups, acetoxyl groups and chlorine, and
n is an integer of up to 3.
The primary coating of the invention is even more preferably obtained by applying and subsequently drying a coating solution containing a plurality of different silicon compounds or their hydrolysates from among silicon compounds and their hydrolysates with an organic functional group represented by general formula (2)
R3nSi(R2)4xe2x88x92nxe2x80x83xe2x80x83(2)
where R3 is an organic functional group with a functional group selected from among methacryloxy, vinyl, allyl and amino groups,
R2 is one or a plurality of hydrolyzable groups selected from among alkoxyl groups, acetoxyl groups and chlorine, and
n is an integer of up to 3.
When the primary coating of the invention is a primary coating obtained from a coating solution containing a plurality of silicon compounds of general formula (2), the properties such as adhesive property onto polyolefin resins is greater compared to using a primary coating obtained from a coating solution containing only a silicon compound of general formula (1).
The present invention also encompasses silicon dioxide-coated polyolefin resins obtained by the aforementioned production process.
[Function]
According to the invention, after hydrophilic treatment of a polyolefin resin, an organic silicon coating is formed and it is then immersed in a silicofluoric acid aqueous solution containing silicon dioxide in a supersaturated state, to form a silicon dioxide coating.
By laying an organic silicon film on the surface of a polyolefin resin by the method described above, it is possible to improve adhesive property between the polyolefin resin that has no functional groups, and silicon dioxide coatings. Here, providing an organic silicon film after hydrophilic treatment of the surface of the polyolefin resin to form a silicon dioxide coating can result in even more reliable improvement in adhesive property between the polyolefin resin and the silicon dioxide coating.
The polyolefin resin used as the base may be a polyalkene such as polyethylene or polypropylene, or a cycloolefin, including the cyclopentene-based open-ring polymer described in Japanese Unexamined Patent Publication No. 168625 of 1994 and the norbornene-based open-ring polymer described in Japanese Unexamined Patent Publication No. 152549 of 1998.
The hydrophilic treatment of the surface of the polyolefin resin base may be carried out by any method that allows hydrophilic treatment of resin base surfaces, and for example, corona discharge treatment, plasma treatment, UV ozone treatment, ozonized water washing and the like may be used for oxidation of the surface. Without this step it is not possible to form a satisfactory coating because of poor adhesive property, even though formation of a silicon dioxide coating is possible. UV ozone treatment, corona discharge treatment, plasma treatment by high frequency plasma discharge and other types of treatment or ozonized water washing can accomplish hydrophilic treatment without impairing the surface of the polyolefin resin. Such treatment methods also have the function of removing dirt and oil from the polyolefin resin surface, in addition to oxidation or activation of the surface. A concrete example of hydrophilic treatment will now be explained.
UV ozone treatment is carried out by irradiation for 1-20 minutes at 20 mW/cm2 in an oxygen-containing atmosphere, with a distance of 20-50 mm between the polyolefin resin base and the UV lamp. The polyolefin resin base maybe rapidly subjected to hydrophilic treatment by heating at 30-100xc2x0 C.
Corona discharge is accomplished by creating a corona discharge between the electrode and the base surface while maintaining a distance of 0.5-8 mm between the electrode and the polyolefin resin base and moving the base under the electrode at a speed of 1-100 mm/sec. The discharge is accomplished in air with application of a voltage of 10-30 kV at a cycle of 15 kHz.
Plasma treatment by high frequency plasma discharge is a method in which a glow discharge is created between the electrode and the base in a reduced pressure oxygen atmosphere, for hydrophilic treatment of the polyolefin resin surface.
Ozonized water washing is a method in which the base is immersed for a few minutes in water that has dissolved ozone having oxidizing property at about a few ppm, for hydrophilic treatment of the surface.
These types of treatment can accomplish hydrophilic treatment of the resin surface. Observation of the elemental composition of the surface by XPS reveals a larger amount of oxygen than before hydrophilic treatment, with the oxygen introduced only near the resin surface in the form of hydroxyl groups, carbonyl groups and carboxyl groups. These functional groups serve as bonding sites with the coating, allowing formation of a satisfactory coating. According to XPS, an elemental ratio of oxygen and carbon (O/C) of at least 0.08 allows formation of a coating with satisfactory adhesive property. The water droplet contact angle of the base surface after treatment has been confirmed to be no greater than about 60xc2x0. Incidentally, the water droplet contact angle of untreated polyolefin resin is around 90xc2x0.
The thickness of the primary coating obtained by applying the coating solution containing a silicon compound or hydrolysate thereof with an organic functional group is preferably 2-50 nm. This thickness range is preferred from the standpoint of providing a uniform coating even on bases with complex shapes, and of achieving improvement in adhesive property with silicon dioxide coatings.
The primary coating thickness will be determined by the concentration of the organic silicon compound in the coating solution and by the application conditions, and these must therefore be appropriately selected. The solvent for the coating solution may be an organic solvent such as alcohol, or water.
The method of applying the primary coating may be dipping, spraying, flow coating or the like.
The silicon compound of general formula (1) is represented by
R1nSi(R2)4xe2x88x92nxe2x80x83xe2x80x83(1)
where R1 is an organic functional group with a methacryloxy group,
R2 is one or a plurality of hydrolyzable groups selected from among alkoxyl groups, acetoxyl groups and chlorine, and
n is an integer of up to 3. The following are specific examples of silicon compounds of general formula (1).
3-methacryloxypropylmethyldichlorosilane,
3-methacryloxypropylmethyldimethoxysilane,
3-methacryloxypropylmethylmethoxyethoxysilane,
3-methacryloxypropylmethyldiethoxysilane,
3-methacryloxypropyldimethylacetoxysilane,
3-methacryloxypropylmethyldiacetoxysilane,
3-methacryloxypropylmethylmethoxyacetoxysilane,
3-methacryloxypropylmethylthoxyacetoxysilane,
3-methacryloxypropylmethoxydiethoxysilane,
3-methacryloxypropylmethoxydiacetoxysilane,
3-methacryloxypropylmethoxyethoxyacetoxysilane,
3-methacryloxypropyldimethoxyacetoxysiane,
3-methacryloxypropyldimethoxyethoxysilane,
3-methacryloxypropyltriethoxysilane,
3-methacryloxypropylethoxydiacetoxysilane,
3-methacryloxypropyldiethoxyacetoxysilane,
3-methacryloxypropyltriethoxysilane,
3-methacryloxypropyltriacetoxysilane,
3-methacryloxypropyltrichlorosilane,
2-methacryloxyethylmethyldichlorosiane,
2-methacryloxyethyltrichlorosilane,
2-methacryloxyethylmethyldimethoxysilane
2-methacryloxyethyltrimethoxysilane,
2-methacryloxyethylmethyldiethoxysilane,
2-methacryloxyethyltriethoxysilane,
2-methacryloxyethylmethyldiacetoxysilane,
2-methacryloxyethylethyldiacetoxysilane,
2-methacryloxyethyltriacetoxysilane,
2-methacryloxyethylmethylmethoxyethoxysilane,
2-methacryloxyethyldimethylacetoxysilane,
2-methacryloxyethylmethylmethoxyacetoxysilane,
2-methacryloxyethylmethylethoxyacetoxysilane,
2-methacryloxyethylmethoxydiethoxysilane,
2-methacryloxyethylmethoxydiacetoxysilane,
2-methacryloxyethylmethoxyethoxyacetoxysilane,
2-methacryloxyethyldimethoxyacetoxysilane,
2-methacryloxyethyldimethoxyethoxysilane,
2-methacryloxyethylethoxydiacetoxysilane,
2-methacryloxyethyldiethoxyacetoxysilane,
methacryloxymethylmethyldichlorosilane,
methacryloxymethyltrichlorosilane,
methacryloxymethylmethyldimethoxysilane,
methacryloxymethyltrimethoxysilane,
methacryloxymethylmethyldiethoxysilane,
methacryloxymethyltriethoxysilane,
methacryloxymethyldimethoxysilane,
methacryloxymethyldiethoxysilane,
methacryloxymethylmethyldiacetoxysilane,
methacryloxymethylmethylmethoxyacetoxysilane,
methacryloxymethyldimethoxyacetoxysilane,
methacryloxymethylmethoxyethoxyacetoxysilane,
methacryloxymethyldiethoxyacetoxysilane,
methacryloxymethylmethylmethoxyethoxysilane,
methacryloxymethyldimethylacetoxysilane,
methacryloxymethylmethylethoxyacetoxysilane,
methacryloxymethylmethoxydiacetoxysilane,
methacryloxymethyldimethoxyethoxysilane,
methacryloxymethylethoxydiacetoxysilane,
methacryloxymethyltriacetoxysilane,
2-methacryloxyethylmethylmethoxyacetoxysilane,
2-methacryloxyethyldimethoxyacetoxysilane,
2-methacryloxyethylmethylethoxyacetoxysilane,
2-methacryloxyethyldiethoxyacetoxysilane,
2-methacryloxyethylmethyldichlorosilane,
2-methacryloxyethylmethyldimethoxysilane,
2-methacryloxyethylmethylmethoxyethoxysilane,
2-methacryloxyethylmethyldiethoxysilane,
2-methacryloxyethyldimethylacetoxysilane,
2-methacryloxyethylmethyldiacetoxysilane,
2-methacryloxyethylmethoxydiethoxysilane,
2-methacryloxyethylmethoxydiacetoxysilane,
2-methacryloxyethylmethoxyethoxyacetoxysilane,
2-methacryloxyethyldimethoxyacetoxysilane,
2-methacryloxyethyldimethoxyethoxysilane,
2-methacryloxyethyltrimethoxysilane,
2-methacryloxyethylethoxydiacetoxysilane,
2-methacryloxyethyltriethoxysilane,
2-methacryloxyethyltriacetoxysilane,
2-methacryloxyethyltrichlorosilane
An ester group is present in the organic silicon-containing coating obtained by silicon compounds or their hydrolysates wherein R1 of the compound of general formula (1) is a methacryloxypropyl group. If an ester group is included in the organic silicon-containing compound, the adhesive property is improved when the silicon dioxide film is deposited on the film from the silicofluoric acid solution, although the reason for this phenomenon is not fully understood.
The silicon compound of general formula (2) is represented by
xe2x80x83R3nSi(R2)4xe2x88x92nxe2x80x83xe2x80x83(2)
where R3 is an organic functional group with a functional group selected from among methacryloxy, vinyl, allyl and amino groups,
R2 is one or a plurality of hydrolyzable groups selected from among alkoxyl groups, acetoxyl groups and chlorine, and
n is an integer of up to 3. The following are specific examples of silicon compounds of general formula (2), in addition to those mentioned above for general formula (1).
vinylmethyldichlorosilane,
vinyltrichlorosilane,
vinylmethyldimethoxysilane,
vinyltrimethoxysilane,
vinylmethyldiethoxysilane,
vinyltriethoxysilane,
vinylmethyldiacetoxysilane,
vinyltriacetoxysilane,
allylmethyldichlorosilane,
allyltrichlorosilane,
allylmethyldimethoxysilane,
allyltrimethoxysilane,
allylmethyldiethoxysilane,
allyltriethoxysilane,
allylmethyldiacetoxysilane,
allyltriacetoxysilane,
3-(N-allylamino)propylmethyldichlorosilane,
3-(N-allylamino)propyltrichlorosilane,
3-(N-allylamino)propylmethyldimethoxysilane,
3-(N-allylamino)propyltrimethoxysilane,
3-(N-allylamino)propylmethyldiethoxysilane,
3-(N-allylamino)propyltriethoxysilane,
3-(N-allylamino )propylmethyldiacetoxysilane,
3-(N-allylamino)propyltriacetoxysilane,
3-aminopropylmethyldichlorosilane,
3-aminopropyltrichlorosilane,
3-aminopropylmethyldimethoxysilane,
3-aminopropyltrimethoxysilane,
3-aminopropylmethyldiethoxysilane,
3-aminopropyltriethoxysilane,
3-aminopropylmethyldiacetoxysilane,
3-aminopropyltriacetoxysilane,
N-(2-aminoethyl)-3-aminopropylmethyldichlorosilane,
N-(2-aminoethyl)-3-aminopropyltrichlorosilane,
N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane,
N-(2-aminoethyl)-3-aminopropyltrimethoxysilane,
N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane,
N-(2-aminoethyl)-3-aminopropyltriethoxysilane,
N-(2-aminoethyl)-3-aminopropylmethyldiacetoxysilane,
N-(2-aminoethyl)-3-aminopropyltriacetoxysilane
Since a primary coating obtained from a silicon compound wherein R3 in general formula (2) has an amino group will include large amounts of amino groups that exhibit powerful interaction with the carboxyl groups or hydroxyl groups on the uppermost surface of the hydrophilic treated polyolefin resin, the interface adhesive property between the resin base and the primary coating is improved.
For example, it is possible to form a uniform silicon dioxide coating even over a primary coating containing only a silicon compound in which R1 of general formula (1) is a methacryloxy group, and to thereby improve the coating adhesive property, as explained above. However, for even more improved coating adhesive property, there may be used a primary coating formed from at least 2 different compounds of the compounds of general formula (2) of the invention.
In the case of a primary coating obtained using only a silicon compound in which R3 of general formula (2) is a functional group with an amino group, the hydrophilic nature of the silicon compound with the amino group results in its elution when the silicofluoric acid solution containing silicon dioxide in a supersaturated state is later contacted therewith to form the silicon dioxide coating, thus inhibiting formation of a uniform film with the silicon dioxide coating.
If the starting material for the primary coating includes a silicon compound in which R3 of general formula (2) is an amino group in combination with a silicon compound containing a reactive group of low hydrophilic nature such as methacryloxy, vinyl or allyl as R3, the subsequent formation of the silicon dioxide coating can be carried out in a uniform manner. While the reason allowing uniform formation of the silicon dioxide coating is not fully understood, it is conjectured that it facilitates orientation of the organic functional groups in the coating toward the resin interface and of the silanol groups toward the silicon dioxide coating.
The amino group-containing silicon compound is preferably in the range of 0.01-70 wt % of the total silicon compounds in the coating solution. If the amino group-containing silicon compound is present at less than 0.01 wt % it may not be possible to achieve an effect of improved adhesive property. On the other hand, it is preferably not greater than 70 wt % because this will prevent the silicon dioxide coating from becoming a uniform film.
However, it is not always necessary to use a substance including a silicon compound wherein R3 of general formula (2) contains an amino group, and several compounds may be used in combination from among methacryloxy, vinyl and allyl group-containing compounds. This will, however, result in slightly inferior adhesive property with the olefin resin, as compared to using, as one of the components, a silicon compound wherein R3 of formula (2) contains an amino group.
The polyolefin resin base with the primary coating formed thereon is contacted with a silicofluoric acid solution containing silicon dioxide in a supersaturated state, to form a silicon dioxide coating on the primary coating. The silicofluoric acid (H2SiF6) solution with silicon dioxide in a supersaturated state (hereunder referred to as the xe2x80x9ctreatment solutionxe2x80x9d) may be prepared with silicon dioxide in the super saturated state by such means as dissolving silicon dioxide (silica gel, aerogel, silica glass or some other silicon dioxide-containing substance) in a silicofluoric acid solution and then adding water or a reagent (such as boric acid, aluminum chloride, metallic aluminum or the like) or raising the temperature of the treatment solution.
According to the invention, the concentration of the silicofluoric acid in the treatment solution that is contacted with the primary coating-applied polyolefin resin molded base is preferably 1-4 moles/liter, and an especially fast coating formation rate, for more efficient coating formation, can be achieved by first saturating silicon dioxide in a silicofluoric acid solution with a concentration of greater than 3 moles/liter and then diluting with water to a concentration of 1-4 moles/liter.
The treatment solution is preferably:
(a) a treatment solution wherein supersaturation is constantly maintained even during contact with the resin base by such means as {circle around (1)} continuously adding and mixing therewith an additive aqueous solution of boric acid or aluminum chloride, {circle around (2)} dissolving and mixing therewith a metal such as aluminum, or {circle around (3)} momentarily cooling the temperature for silicon dioxide saturation and then raising the temperature again, and
(b) a treatment solution wherein at least 3% of the total amount of treatment solution is filtered through a filter per minute, and circulated.
From the standpoint of improving the coating formation rate it is preferred to {circle around (1)} continuously add and mix an aqueous solution of boric acid or the like or {circle around (2)} dissolve and mix a metal such as aluminum, during contact with the resin base. For boric acid, the amount added is preferably in the range of 5xc3x9710xe2x88x924 moles/hr to 1.0xc3x9710xe2x88x923 moles/hr with respect to one mole of the silicofluoric acid in the treatment solution, and for dissolution of metallic aluminum, the dissolution amount is preferably in the range of 1xc3x9710xe2x88x923 moles/hr to 4xc3x9710xe2x88x923 moles/hr with respect to one mole of the silicofluoric acid in the treatment solution.
Circulation of a treatment solution with a silicofluoric acid concentration of at least 3% is effective in order to continuously obtain a uniform coating, and filtration of the treatment solution with a filter is preferred in order to obtain a coating with no irregular shapes.
When the treatment solution is placed in an immersion tank for contact with the resin base, a smooth uniform coating can be effectively obtained if the treatment solution is circulated by laminar flow on the surface of the immersed base resin.
The silicon dioxide coating obtained by such a deposition method will contain adsorbed moisture and silanol groups, and these are preferably removed by heat treatment of the coating with high frequency waves.
Since it is thereby possible to form a silicon dioxide coating with excellent adhesive property on the polyolefin resin surface, the highly adhesive silicon dioxide coating inhibits release of the trace gases (plasticizer, H2O, etc.) in the resin, thus enhancing the excellent features of the polyolefin resin such as low moisture absorption, heat resistance, chemical resistance and the like, and rendering it suitable for such uses as optical parts, electronic parts and automobile parts.
In particular, since release of trace gases in the resin is inhibited by the highly adhesive silicon dioxide coating even when a magnetic film is formed on the silicon dioxide coating, there is no risk of deteriorated crystallinity of the magnetic film due to release of the trace gases. The present invention products therefore have even greater potential for use in electronic devices such as magnetic recording media.
The silicon dioxide-coated polyolefin resin obtained according to the invention can be applied to personal and industrial use electronic devices including plates for magnetic disks (HDDs, etc.) and to optical lenses, optical fibers, optical disks and other optical devices, as well as to the various products mentioned below.
Because of the excellent electrical insulating properties of polyolefin resins, their applications include coating materials for wiring and cables, and general insulating materials for OA devices such as copy machines, computers, printers and the like and measuring instruments; circuit boards such as hard printed circuit boards, flexible printed circuit boards and multilayer printed wiring boards, as well as high frequency circuit boards for satellite communication devices which require particularly high frequency properties; base materials for transparent conductive films and sheets in liquid crystal panels, optical memories, and surface heaters such as defrosters for automobiles and aircraft; semiconductor sealing materials and parts for transistors, ICs, LSIs, LEDs and the like; sealing materials for electric and electronic parts such as motors, connectors, switches and sensors; body materials for television sets and video cameras or housing materials for various measuring instruments; structural members for parabolic antennas, flat antennas, radar domes and the like; as well as films, sheets, helmets, etc.